No it is not a simple plug and play. Personally, I took the long route and studied the wiring diagrams, then cut and resoldered all the harness ends, using the 280ZXT harness. If you are patient and meticulous you can get good results - mine has been trouble-free. If you are not into wiring, you can use the Z31 harness, possibly having to relocate the ECU to the passenger side - not a bad option IMHO. Other people have figured out how to use the 280ZXT harness as-is, with some connector modifications. A friend of mine tried that, and ended up connectiong the MAF backwards, and cooked the ECU - risky.
None of the Nissan ECUs are speed-density. The L28 stuff (280Z, 280ZX, 280ZXT) all have the door-flap air flow meter, and the Z31s use a hot wire MAF for air measurement. This is a much less restrictive way to measure air - the door-flap is crap.